1. Field of the Invention
The present invention relates to a thrust needle roller bearing for use in a compressor of an air conditioner of an automobile.
2. Description of the Background Art
A thrust needle roller bearing is formed of needle rollers, a retainer and a bearing washer, and the needle rollers make line-contact with the bearing washer so that it can achieve a high load capacity and a high rigidity although a bearing projection area is small. Therefore, the thrust needle roller bearings have been widely used as structures for bearing thrust loads in compressors of air conditioners of automobiles. Conditions of use are becoming more severe due to driving with lean lubrication or high-speed rotation.
For example, Japanese Patent Laying-Open No. 2002-70872 has disclosed a conventional thrust needle roller bearing, in which inflow and/or outflow properties of lubricant or lubricating oil are improved for increasing an amount of lubricant supplied per time. This thrust needle roller bearing will now be described with reference to FIGS. 21A–21C.
Referring to FIGS. 21A–21C, a thrust needle roller bearing 50 is formed of a plurality of needle rollers 80 and two annular retainers 60 and 70. Each of two retainers 60 and 70 has a plurality of long windows 61 or 71, each of which is radially longer than roller 80. These plurality of windows 61 and 71 provide roller retaining portions 64 and 74, which retain the plurality of needle rollers 80 in the vertically opposite directions. Each of roller retaining portions 64 and 74 of two retainers 60 and 70 has a radial length 1a shorter than a roller length 1. At least one of two retainers 60 and 70 is bent by appropriate working so that at least one of total thicknesses or vertical lengths t1 and t2 of radially outer and inner portions of retainers 60 and 70 is smaller than a total thickness t0 of roller retaining portions 64 and 74.
Radially outer plate portions 62 and 72 of two retainers 60 and 70 vertically are overlaid with each other, and end portions 67 and 77 of radially inner plate portions 63 and 73 of retainers 60 and 70 are vertically bent to overlap with each other, and are fixed together by caulking effected on end portion 67 of radially inner plate portion 63.
This structure improves the inflow and/or outflow properties of lubricant in at least one of the radially outer and inner portions, which have reduced thicknesses as compared with roller retaining portions 64 and 74, and thereby can increase the amount of lubricant passing through the bearing per time. Further, such a situation is suppressed that retainers 60 and 70 intercept the passing lubricant. Therefore, the lubricant does not remain, and increase in lubricant temperature can be suppressed so that durability of the bearing can be improved.
For ensuring intended strengths of retainers 60 and 70 as well as needle rollers 80 in the thrust needle roller bearing 50, two retainers 60 and 70 as well as needle rollers 80 are made of a cold-rolled steel plate (SPCC). Thus, thrust needle roller bearing 50 is primarily made of iron so that it suffers from a problem of a large weight. Since the weight of thrust needle roller bearing 50 is large, an inertia weight and thus inertia force are large so that a large torque loss occurs, e.g., in an automobile air conditioner or a compressor. This deteriorates the fuel consumption.
Since two retainers 60 and 70 as well as needle rollers 80 are primarily made of iron, large friction unpreferably occurs between needle rollers 80 and two retainers 60 and 70. The large friction between needle rollers 80 and two retainers 60 and 70 increases a required torque and noises during rolling of needle rollers 80.
Further, in the operation of the conventional thrust needle roller bearing 50, a peripheral speed of a raceway surface in contact with needle roller 80 increases as the position moves radially outward in thrust needle roller bearing 50. Therefore, a difference in peripheral speed between needle roller 80 and the raceway surface becomes maximum at the opposite end surfaces of needle roller 80. This tendency increases with increase in relative length of the needle roller with respect to the outer diameter. This peripheral speed difference causes differential sliding on needle roller 80. Thereby, heat is generated from contact portions of needle rollers 80 and the raceway surface so that surface damage (smearing) and/or surface-starting peeling occur. Since these phenomena are liable to occur in the conventional thrust needle roller bearing, it may also suffer from insufficient durability.